When an oil well is drilled a string of casing is positioned in the well borehole extending from the earth's surface to the producing formation. In many instances when a borehole penetrates an oil bearing formation, bottomhole pressure of the formation is sufficient to cause crude oil to flow from the formation to the earth's surface. In many parts of the world, however, the bottomhole pressure is not substantial or long lasting, and when the pressure drops to that which is insufficient to force crude oil to the earth's surface some means must be provided for pumping the well. For this reason, reciprocating bottomhole pumps have been employed from the beginning of the petroleum industry.
In the typical oil well pumping arrangement, a pump jack is positioned at the earth's surface that reciprocates a long string of sucker rods within a tubing string. A bottomhole pump is positioned within the tubing string. The typical bottomhole pump includes a stationary barrel affixed to or removably attached to the tubing. Positioned within the stationary barrel is a reciprocating plunger affixed to the lower end of the sucker rod string. A standing or stationary valve, usually in the form of a ball and seat, is typically affixed to the lower end of the barrel and a traveling valve is secured to the plunger, the traveling valve also typically being a ball and seat.
In this arrangement, on the upstroke of the sucker rod string the plunger is pulled upwardly within the barrel, closing the traveling valve and drawing fluid within the barrel through the open standing valve. On the downstroke of the plunger the standing valve closes and fluid within the plunger passes upwardly through the traveling valve, through the interior of the plunger and out above the plunger. On the succeeding upstroke the fluid above the plunger is forced upwardly, past the upper end of the barrel into the interior of the tubing and ultimately to the earth's surface. The valves support the entire weight of the fluid column from the pump to the earth's surface, and, therefore, the typical reciprocated bottomhole pump must, according to the depth of the pump, withstand considerable fluid pressures.
The efficiency and effectiveness of the pump depends upon a very close fit between the exterior plunger pump surface and the barrel interior cylindrical surface. When fluid leakage occurs between these surfaces efficiency of the pump is reduced and if substantial fluid flow occurs between the exterior plunger surface and the interior barrel surface, the pump can become totally defective. The problem of pumping crude oil is that in some locations substantial components of sand or other abrasives are entrained within the crude oil fluid. Most oil producing formations are of relatively high porosity and are formed of compacted sand granules, and some of the sand granules become dislodged from the formation as the fluid is extracted from it. Abrasives also originate from scale, mineral deposits and other sources. Since most reciprocating downhole pumps are made of metal, that is, a metal barrel and a metal plunger, there is metal to metal contact as the plunger is reciprocated within the barrel. If sand is entrained within the crude oil fluid, the abrasive effect can soon wear a pump plunger to the point where the well efficiency drops below an acceptable level.
In addition to the arrangement hereinabove described of a stationary barrel and a reciprocating plunger, in some instances this relationship is reversed, providing a stationary plunger and a reciprocating barrel. In addition, the valving arrangements for bottomhole pumps can be varied considerably. However, a common characteristic of reciprocating bottomhole pumps is that in order to move fluid from an oil bearing formation to the earth's surface, a plunger and a barrel must be reciprocated relative to each other.
An object of this invention is to provide an improved pump plunger having longer wearing characteristics and one that is especially adaptable for use in sandy environments.